Boston, Mass.-based neurologist Joel Salinas is a doctor who knows exactly how you feel. Perfectly attuned to the sensations of others, the 33-year-old has a condition known as mirror-touch synesthesia, in which the section of his brain wired to empathy and social perception is believed to be much more active than that of a typical person’s. His book, “Mirror Touch: Notes From a Doctor Who Can Feel Your Pain” (HarperOne, out Tuesday), chronicles what it’s like to live with these phantom experiences. Here, Salinas tells The Post’s JANE RIDLEY about this incredible “superpower.”

Meeting a nonverbal woman with cerebral palsy who has become agitated and combative with the medical staff, I’m struck by a quickening of my breath. The sensation of suffocating is almost overwhelming and I experience the sensation that something is wrong with my lungs. I order a series of tests on her. Turns out she has blood clots — on her lungs.

I honestly don’t think I would have picked up on this diagnosis had it not been for mirror-touch synesthesia, a fascinating — and sometimes troublesome — neurological trait that causes me to feel the emotional and physical sensations of other people.

If someone has a migraine, for example, there will be a heaviness in my head. When I’m assisting with childbirth, phantom contractions go through my abdomen. If a fellow subway passenger is experiencing depression, [his or her] anxiety rubs off on me.

Mirror-touch synesthesia can be helpful when making diagnoses, says Dr. Salinas.Matthew Healey

Nobody knows what causes mirror touch, though researchers have isolated evidence of synesthesia — a general neurological phenomenon where when one sense is sparked, another one is almost simultaneously set off — in the brain using MRIs. It appears that it’s related to an increase in activation of the mirror neuron system, with greater connectivity in parts of the brain tied to social perception and empathy [and] less connectivity in parts of the brain responsible for making the distinction between ourself and others — with the brain likely treating another person’s body as if it were its own.

I also have another form of synesthesia called chromesthesia, common among musicians [see sidebar below], in which I perceive sound with color and, in another manifestation, motions with sound.

It was 2005, when I was 23, when I discovered I had the trait after researching scientific literature. I read about scientists who specialize in the subject at Goldsmiths College, University of London and the University of Sussex in the UK, and traveled over to England to have neurological tests done by them in 2014.

Until I discovered about synesthesia, I just thought I was an unusual kid. Growing up in Miami, I’d watch cartoons like the Road Runner, and if Wile E. Coyote was squashed by a boulder, I’d feel compacted as if I were an accordion.

As I got older, the synesthesia became more problematic. I remember watching a [physical] fight between two girls at my high school. I felt tension in my scalp as if I were being grabbed by the hair. They were clawing at each other and it felt like arrowheads scraping against my face.

So why did I pursue a career in medicine, where I’d routinely be exposed to people in distress? A key reason was being a synesthete. Sharing in the pain and suffering of others makes the patient feel a little less alone and also the synesthete can reason through the experience and respond with compassion and kindness. The motivation to help others has silently guided me all this time, whether as a student, resident or neurologist, as I am now.

Anecdotally, I’ve heard that synesthetes do tend to go into caring professions, possibly because by helping people they’ll feel better themselves. One friend who has mirror-touch synesthesia became a masseuse, for instance.

Sharing in the pain and suffering of others makes the patient feel a little less alone … The motivation to help others has silently guided me.

But it hasn’t been easy for me. In my first week as an internal-medicine clerk, a man was found on the floor suffering cardiac arrest. As the team worked to save his life, I was fully immersed in his bodily experience. I felt as if my back was pressed against the linoleum floor, my limp body buckling under each compression, my chest swelling with each artificial breath squeezed into it. I was dying, but I was not.

In the case of [a] heart-attack patient, I rushed to the bathroom and vomited after the time [of death] was called. But I have rarely had such a severe, visceral reaction since. As for witnessing death, I can only describe my reflections by likening it to sitting for hours in a room with an air conditioner on and, the moment that it stops, you really notice it was running. There’s this eerie silence. All the movements that have been constantly reenacted on my body stop. At that moment, I almost have to will myself to breathe.

The way I dissipate the mirror-touch experiences and compartmentalize is to focus on something that doesn’t look like a human body or have emotions. A doorknob, or a sleeve, for instance. Sometimes, it means me focusing on my own body, thinking about the sensations of my toes like you do in meditation. I might also stare into a mirror.

Avoiding eye contact helps. That way, I can really listen to a conversation without so much of a sensory component. But it has caused problems in my personal relationships. My ex-husband, Jordan, from whom I divorced a year ago, thought I wasn’t paying attention to him when it was just the opposite.

The big flip side of synesthesia is that. being around a romantic partner so much, you constantly reflect their physical and emotional sensations. It’s as if my brain’s body mass extends into theirs. Separating the two is hard. Fortunately, I’ve learned a lot from past relationships and I’ve learned to detach from the other person’s experiences. I’m much freer, moving between my own self and theirs. I have more boundaries now but they are thoughtful boundaries.

What’s helped me is to approach other people’s experiences as a curiosity, not a threat. If I want a pick-me-up, I’ll look at somebody who is having a good time. A couple hugging. A baby laughing. It’s the most amazing feeling to experience the delight of a baby.

Synesthesia has been a harsh, but just, teacher. There is suffering and pain, but, at the same time, so much joy and love that can be experienced, too.

Billy Joel is just one celeb known to have synesthesia.Myrna M. Suarez/Getty Images

Stars with synesthesia

Around 4 percent of the general population has some form of synesthesia, including chromesthesia, in which people perceive sound as colors. Below are six artists who are believed to have, or have had, a version of the condition.

Jimi Hendrix
Urban legend has it that Hendrix named “Purple Haze” after the color of a chord.

Marilyn Monroe
Norman Mailer wrote she had “a displacement of the senses that others take drugs to find.”

Billly Joel
The pop star said, “When I think of different types of melodies, I think in terms of [colors].”

Vladimir Nabokov
The “Lolita” writer had grapheme-color synesthesia, and perceived letters as colors.

Stevie Wonder
Despite being blind, the singer has been said to “see” the color of his music.